Participants in this research study will include patients with a vision problem (retinitis pigmentosa or a related disorder) due to a loss of the function of their retinas (the back part of the eye). Participants may also include people with normal vision to act as a "normal control" for patients with the above described eye diseases. The aim of this research investigation is to examine the concentrations of a unique class of highly polyunsaturated fats, the n-3 fatty acids. It is likely that these fatty acids play a role in vision. One of these fatty acids, docosahexaenoic acid (DHA), is normally found in high concentration in the retina, sperm and brain. Abnormalities of DHA concentration may be a component of retinitis pigmentosa in some patients. The purpose of this study is to examine the differences in DHA (and other n-3 fatty acids) concentrations in subjects with retinitis pigmentosa and controls and to determine if DHA concentrations increase significantly in the blood due to feeding the precursor fat linolenic acid from flaxseed oil. Flaxseed oil feeding will last for a period of 12 weeks.